In the modern world plastics are the material of choice for the manufacture of a seemingly unlimited number of products. These products are produced by a variety of industrial processes, e.g. injection molding, blow molding, extrusion, and 3-D printers. The raw material that is fed into the machines used to produce the final products is a mixture consisting of: polymers (called resin in the industry), colorants and other additives, e.g. UV inhibitors, all in the form of small beads. The colorants and other additives are supplied as masterbatches, which are concentrated mixtures of pigments and/or additives encapsulated during a heat process into a carrier resin which is then cooled and cut into a granular shape.
Today it is customary in the plastic industry to feed the processing machines e.g. injection molding machines, blow molding machines, extrusion machines, either with premixed plastic formulations or, as it is applied in most of the cases, by feeding the processing machines directly by means of gravimetric blenders that weigh and blend the various components based on their weight settings. In a large facility a common way to deliver mixtures of raw materials is as follows: The premixed formulations are prepared in a Remote Central Gravimetric Blenders (RCGB) by mixing resins, colored masterbatch and additives by each of its gravimetric blenders to achieve the desired qualities and color and then transported to the individual processing machine. In some cases the colored masterbatch is fed directly to the neck of the processing machine by a single component gravimetric or volumetric feeder.
Typically a large manufacturing facility comprises many processing machines in order to be able to simultaneously produce several different products. In order to do this a large facility can have a RCGB that is comprised of many gravimetric blenders, each of which is feed with the required type of raw material from a plurality of storage silos. The RCGB is a complex of gravimetric blenders each of which comprises several bins, i.e. hoppers or several compartments in a hopper. The number of components each gravimetric blender is capable of blending depends on the number of its bins. On each bin is installed a hopper loader feeder in order to convey into it raw materials from the proper silo.
When the gravimetric blender operates, the unit desirably operates automatically, adding each of the component solid materials in the proper, desired weight. Each solid material component is dispensed by weight into a single weigh bin. Once the proper amount of each component has been serially dispensed into the weigh bin, all of the components are dropped together into a mixing chamber from the weigh bin.
When mixing in the mixing chamber is complete, the resulting blend can be provided to an interim container preferably underneath the blender, used as a buffer and then passes through an automatic manifold that automatically allows every blend produced by a defined remote gravimetric blender to be conveyed through a pipe to any chosen processing machine that is related to the same automatic manifold. The automatic manifolds are in principle constructed at least from two similar base units connected via a pipe. One of the base units is connected to the inlet pipes that arrive from the gravimetric blenders or its buffers and the other is connected to the outlet pipes that are connected to the processing machines.
FIG. 1 schematically shows a typical prior art RCGB 10 comprised of four or more gravimetric blenders 12. Each gravimetric blender 12 comprises four bins 14, which are fed with the required raw material from one of six or more silos 16. Material from each bin 14 drops into weighing hopper connected to load cell 18. The material from each bin is weighed separately in serial fashion and only when the required amounts of all of the materials have been weighed is the batch allowed to drop into mixer 20, which is then activated. After the batch has been thoroughly mixed it drops into a buffer or to an automatic manifold 22 and is routed to the correct process machine 24.
FIG. 2A and FIG. 2B are drawings symbolically showing a RCGB at a large manufacturing plant for producing plastic products. Seen in the drawings are an overall view of the RCGB in FIG. 2A and the automatic manifolds of the gravimetric blenders with pipes leading from the mixers into the manifold at the top and pipes leading to the process machines at the bottom of the manifolds in FIG. 2B.
The prior art RCGB has a number of disadvantages:                1. Cost—A typical RCGB for a plant that comprises ten silos to hold different raw materials to blend batches that comprise no more than four of the raw materials to supply 100 injection machines can require for example 60 four-bin gravimetric blenders in order to have maximum adaptability.        2. They occupy a great deal of space. The RCGB just described would require 200-300 of square meters of floor space.        3. Complexity—FIG. 2B gives a brief glance at the large number of delivery pipes that run from the manifolds to the 100 processing machines. In addition each of the 240 bins in the gravimetric blenders is connected to one of the ten silos. Installation and maintenance of this complex piping system is time consuming and expensive.        4. Possibility of contamination—To produce high quality products having consistent properties such as strength and color the weight of each component of the batch must be very carefully controlled and in some instances contamination by only a few beads of material can affect the properties of the product. If it is desired to change the type of material in one or more of the bins in a gravimetric blender, then that blender's operation must cease and a cleaning process carried out in order to prevent contamination.        5. Uniformity of batches that arrive at the production machines—Although each batch is thoroughly mixed before it enters the manifold, as it travels through the delivery pipe to the production machine, typically by means of a vacuum conveying system, the various ingredients can separate out because of the difference in specific weight of the beads.        6. Speed of production—Because the prior art gravimetric blenders weigh each of the up to four components of a batch in serial fashion it takes a relatively long time for each batch to be prepared and fed to the automatic manifold. In addition there is the down-time of parts of the system required for cleaning to prevent contamination.        
Many of these disadvantages of the prior art have addressed in co-owned Israeli Patent Application IL230756, titled Weighing and Feeding System, filed on Jan. 30, 2014.
Unlike a prior art gravimetric blender, in which each component is dispensed separately into a common single weighing chamber and then all components are dropped into a mixing chamber which delivers a homogenous blend to the processing machine, the system of the invention is equipped with a weighing chamber for each component. Therefore the weighing will be done in parallel, thus enabling the use of much smaller load cells and accordingly much better accuracy, yet with a relatively high throughput.
FIG. 3 is a schematic perspective view of the system described in IL230756. The system 30 is a modular one that can be comprised of one or more weighing units 32 arranged in a way that allows the material weighed in each of the units to fall through individual chutes 34 via a common funnel into a mixing machine 36, that combines the output of all of weighing units 32 into a uniform mixture that can be fed into a processing machine. Herein the system 30 is described as one that comprises 12 weighing units 32; however, this is for purposes of illustrating the invention only and, as said, the system can comprise more or less than 12 of these units. Each of the weighing units 32 contains a different type of resin, masterbatch, or additive in granular form. A computer (not shown in the figures) controls the operation of each of the separate weighing units 32 in order to supply the exact weight of each of the individual components to the mixing machine. To prepare a given mixture, the computer will activate only the weighing units 32 that contain the material required for that mixture according to a formulation that has been preloaded into the computer.
Each weighing unit 32 comprises a hopper loader 38 that draws one type of material, i.e. resin, masterbatch, or additive, from a raw material silo into material hopper 40. Hopper 40 has an opening with a flap at its bottom, which is opened and closed when required by an element (not shown in the figure) that is controlled by a system computer (not shown in the figure) to allow a controlled amount of material to fall by gravity into weighing station 42 (hidden behind cover panels 44 where it is weighed on a load cell. When the weight of the material introduced into weighing station 42 and weighed by the load cell is equal to the required weight, then the system computer closes the flap at the bottom of hopper 40 and opens a flap at the bottom of weighing station 42 to allow the material to flow by gravity through chute 34 into mixer 36, where the material is joined by material of other types that has been weighed in parallel by other independent weighing units 32. The combined materials are then mixed thoroughly in mixer 36 and then sent through a manifold to a designated processing machine.
One of the systems 30 described in IL230756 can replace a prior art RCGB comprised of several gravimetric blenders described herein above. Despite the considerable savings in floor space, complexity, and cost made possible by this system, it does not solve all of the problems.
It would be very advantageous for a plastic processing company to have a system for weighing mixtures of material and distributing them to processing machines that overcomes all of the above identified drawbacks of prior art RCGB systems.
It is therefore a purpose of the present invention to provide such a system.
Further purposes and advantages of this invention will appear as the description proceeds.